In the past, when I have ordered a list of items from Screwfix that
exceeded the £45 free-post trigger point, if some of the items were
Nil Stock they would be sent later, post-free (for both Trade Counter
and Web orders).

Apparently there has been a change of policy, and now you will have to
order those Nil Stock items again. This will mean another visit the
Trade Counter, or pay the postage costs if under £45 and orderering
over the Web.

CRB